This invention relates to a device for uniformly measuring log bolts to be cut from a log, for example, and is adapted for attachment to a cutting saw such as a chain saw. More particularly, the device includes a rack and pinion gear assembly for unwinding the coiled tape from a drum, the pinion gears being gear coupled with the drum axle. And, rollers engage the turns of the tape during unwinding for reducing friction between the turns. Some known chain saw measuring devices include the use of rigid rods of a predetermined length, although such devices are limiting in that rods of different lengths must be substituted each time log bolts of different sizes are to be cut. Besides, these devices are cumbersome and may present a safety hazard during the handling and operation of the chain saw. Other known measuring devices include the use of a flexible tape which must be manually uncoiled and hooked onto the end of the log to be cut. It is apparent that use of such other devices is likewise cumbersome, unsafe and of limted design. A further known measuring instrument includes a measuring tape coiled on a drum, the tape being unreeled and reeled by a drive selectively coupled with the chain saw motor. Such a device, however, is not only cumbersome but is not adaptable for attachment to a conventioal chain saw.